This Stretchy Metal Will Change The Future Of Electronics

Flexible electronics are the gateway to a new generation of
phones, brain implants, artificial limbs, solar cells, and
limitless other devices that benefit from the ability to bend,
fold, and rollup.

The problem is figuring out how to make them.

Stretchability and conductivity are difficult properties to
combine. Materials that are good conductors do not stretch well
and materials that do stretch well are not good conductors.

This happens because the stretching of solid material lengthens
chemical bonds, changing the distance between atoms, and in turn,
decreasing conductivity. Alternatively, the crystalline
structures of metals, which makes them good conductors of heat
and electricity, are hard to mold since their internal bonds are
not very forgiving.

"This is the story throughout the entire family of stretchable
conductors," said study researcher Nicholas Kotov, a professor of
engineering at the University of Michigan, who may have developed
the best stretchy conductor yet.

The new material is made from gold nanoparticles that are
embedded in a flexible synthetic material called polyurethane.
The bendy film, described in a paper published in Nature on Wednesday, July 17, can conduct
electricity even when stretched to more than twice its original
length.

Scientists used electron microscope images to see what happened
when the material was stretched. It turns out that the gold
nanoparticles aligned into chains when pulled — instead of
becoming disorganized — creating a good conducting pathway.
Importantly, the nanoparticles rearranged themselves when the
strain was released, meaning the process is reversible.

The gold nanoparticles are
produced in the lab, represented by this deep purple
substance.Michigan
Engineering

The secret lies in the gold nanoparticles, which were made in the
lab so that they they would have a very thin shells on their
surface. The thin shells are much better than thicker traditional
shells.

"This is important because the shell stabilizes the particles and
typically prevents the transfer of electrons from one
nanoparticle to the other," Kotov told Business Insider.

Without a thick shell, the electrons can hop from one
nanoparticle to another more easily and are able to conduct
electricity very well.

The practical applications of elastic metal are far-reaching, but
Kotov is particularly interested in how his material can be used
to improve medical devices.

There are a number of implantable devices for the brain, heart,
and muscles. The problem with these rigid electrodes is that the
human tissue easily recognizes them as foreign materials and
generates scar tissue as a response, explains Kotov. The scar
tissue reduces the performance of implantable devices. A pliable
material that is more akin to our soft tissue is key to
longer-term implants.

The search for a material that has the unusual combination of
stretchability and electrical conductivity is ongoing, but this
is a critical step forward.